The present invention relates to a network interconnection device for interconnect networks of different types or different protocol, and more in particular to a network interconnection device for (i) interconnecting a plurality of the same type of networks through a different type of network to communicate a message from a terminal of a type of network through a different type of network to the terminal of the same type of network, or (ii) communicating a message from a terminal of a type of network to a terminal of a different type of network.
The application is based on Japanese Patent Application No. 10-26761, filed Jan. 23, 1998, the content of which is incorporated herein by reference.
In this network interconnection device, a message in a network of a control system is sent to a network of another control system through an internet or an intranet, or to an device connected to an internet or an intranet, for example, in an environment comprising a plurality of control system networks are connected to each other by an internet or an intranet. This network interconnection device includes a router for sending a message communicated in a given network to a destination through another network of the same type, a gateway for sending a message to a destination through a different type of network, or an event processing device for sending not a data but an event through a network to a destination.
FIG. 1 shows a conventional system for interconnecting different types of network by a router. Consider the case where a message is sent from a node ND1 in a network LAN1 having a first structure (address structure, message format structure, etc.) through a network INET of a second structure to a node ND2 in another network LAN 2 of the first structure. A router xcex1 is connected to the network LAN1 of the first structure that has received the message and the network INET of the second structure has a node ND2 as a message destination in another network LAN2 of the first structure. If the router a determines that the destination of the message is the node ND2, it cannot transmit the message through the network INET of the second structure as it is. Therefore, the router xcex1 transforms the message to suit the network INET of the second structure (by adding an address of a router xcex2 expressed by the second structure or transforming the communication protocol), so that this message can be sent to the router xcex2 connected to another network LAN2 of the first structure and the network INET of the second structure. The router xcex2 retransform the received message into a form suiting the network LAN of the first structure (by deleting the address of the router xcex2 of the second structure or inversely transforming the communication protocol). In this way, the message is sent to the intended destination address (ND2).
Specifically, it is assumed that a control network LON (which is based on LonTalk protocol, LON and LonTalk are registered trademarks of Echelon corporation) is constructed in a factory A as a network LAN1 of the first structure, and another control network LON is constructed in a factory B distant from the factory A. It is desired to exchange data between the control networks LONs of the factories A and B through another type of network such as an internet or an intranet connected thereto.
The problem of this system is that the node ND3 of the network INET of the second structure or a plurality of nodes (in whichever of the networks) including the original destination node cannot receive the message. This is because that each network (the control network LON, for example) controls the nodes associated with it but does not control the nodes associated with other types of network, and therefore a destination cannot be specified. In recent years, demand has grown that control networks LON confined in respective floors of a building be connected to each other through an intranet or an internet or that control networks LON installed separately in distant factories be connected for transmission by an intranet or an internet. Further, demand is rising that the data exchanged in this way between the terminals of the networks be sent/received and managed at the terminals of an administration division of the head office through an intranet or an internet. The resulting demand is for sending a message to or receiving a message from a terminal of a different type of network without being conscious of the difference of network type.
Accordingly, it is an object of the present invention to provide a network interconnection device for a network system including different types of networks, wherein a message can be sent to a plurality of terminals of a different type of network and/or the same type of network through a different type of network from a terminal of a given type of network.
A related object of the present invention is to provide a network interconnection device for permitting sending a message from a terminal of a given type of network to a terminal of a different type of network in a network system including different types of networks.
According to a first aspect of the invention, there is provided a network interconnection device connected to first and second networks, comprising:
a transfer address table for storing a plurality of transfer addresses of the structure of the second network for each message of the first network; and
an address converter for changing the address of a message received from the first network, which address is the address of the structure of the first network, on the basis of the transfer address table, and sending the message to the second network.
The first aspect of the invention permits one-to-multiple address conversion between different types of networks.
According to a second aspect of the invention, there is provided a network interconnection device connected to first and second networks, comprising:
an event table for storing an event identifier for each message of the first network;
a message/event converter for converting a message received from the first network to an event based on the event table; and
an address converter which, upon receipt of an event from the message/event converter, changes the address of a message corresponding to the event, which address is the address of the structure of the first network, to the address of the structure of the second network and sends the event to the resulting address of the second network.
The second aspect of the invention permits communication of a message between different types of networks by an event which is not dependent on the network structure, and realizes a multipurpose message conversion.
According to a third aspect of the invention, there is provided a network interconnection device connected to first and second networks, comprising:
an event table for storing an event identifier for each message of the first network;
a message/event converter for converting the message received from the first network in to an event based on the event table, the converter outputting an event with an event identifier attached thereto; and
means for reading an address from the address table based on an event identifier upon receipt of the event from the message/event converter and changing the address of the message corresponding to the event, which is a system address of the first network, to the address read.
The third aspect can determine the destination based on an event identifier and increase the processing speed.
According to a fourth aspect of the invention, there is provided a network interconnection device for interconnecting first and second networks of a network system, comprising:
a transfer address table for storing a plurality of transfer addresses constituting the addresses of the structure of the second network for each message in the first network;
an address converter for changing the address of a message received from the first network constituting an address of the structure of the first network based on the transfer address table and sending the message to the second network;
a time table for storing the last time point when a message is received from each of other network interconnection devices and the last time point when the message is sent to each of other network interconnection devices;
an alive notification section for sending an alive notice to other network interconnection devices connected to the network that has not sent a message for at least a first predetermined time length based on the time table and updating the last time point of transmission in the time table to the present time; and
an address table update section for detecting other network interconnection devices that have not sent a message for at least a second predetermined time length based on the time table, and deleting the transfer address corresponding to the network interconnection device detected from the transfer address table.
The fourth aspect deletes the network interconnection device as a destination that has not sent a message for a predetermined time length and prevents wasteful transfer, and therefore the load of the network is reduced for an improved efficiency.
According to a fifth aspect of the invention, there is provided a network interconnection device for interconnecting first and second networks of a network system, comprising:
a transfer address table for storing a plurality of transfer addresses constituting the addresses of the structure of the second network for each message of the first network;
an address converter for changing the address of a message constituting an address of the structure of the second network for each message, which address is received from the first network, based on the transfer address table and sending a message to the second network;
an update request section for sending an addition request for registering a set of a desired message and its own address in other network interconnection devices as a transfer address; and
an update section for adding an address of other network interconnection devices to the transfer address table upon receipt of the addition request from the other network interconnection devices.
The fifth aspect automatically updates the transfer address table of each network interconnection device newly connected or reconnected to a network.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.